Triphenylphosphine oxide

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Triphenylphosphine oxide
Triphenylphosphine oxide
Triphenylphosphine oxide
Sample of Triphenylphosphine oxide.jpg
Preferred IUPAC name
Other names
Triphenylphosphine oxide
3D model (JSmol)
ECHA InfoCard 100.011.217
RTECS number SZ1676000
Molar mass 278.29 g/mol
Appearance white crystals
Melting point 154 to 158 °C (309 to 316 °F; 427 to 431 K)
Boiling point 360 °C (680 °F; 633 K)
Solubility in other solvents polar organic solvents
Main hazards slight
R-phrases (outdated) 22-36/37/38
S-phrases (outdated) 26
Related compounds
Related compounds

P(C6H5)3; POCl3; PCl5

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Triphenylphosphine oxide (often abbreviated TPPO) is the chemical compound with the formula OP(C6H5)3, also written as Ph3PO or PPh3O (Ph = C6H5). This colourless crystalline compound is a common side product in reactions involving triphenylphosphine. It is a popular reagent to induce the crystallizing of chemical compounds.

Structure and properties[edit]

Ph3PO is tetrahedral molecule related to POCl3.[1] The oxygen center is relatively basic. The rigidity of the backbone and the basicity of the oxygen center make this species a popular agent to crystallize otherwise difficult to crystallize molecules. This trick is applicable to molecules that have acidic hydrogen atoms, e.g. phenols.[2]

As a by-product of organic synthesis[edit]

Ph3PO is a by-product of many useful reactions in organic synthesis including the Wittig, Staudinger, and Mitsunobu reactions. It is also formed when PPh3Cl2 is employed to convert alcohols into alkyl chlorides.

Ph3PCl2 + ROH → Ph3PO + HCl + RCl

Triphenylphosphine can be regenerated from the oxide by treatment with trichlorosilane.

Ph3PO + SiHCl3 → PPh3 + 1/n (OSiCl2)n + HCl

Triphenylphosphine oxide can be difficult to remove from reaction mixtures by means of chromatography. It is poorly soluble in hexane and cold diethyl ether. Trituration or chromatography of crude products with these solvents often leads to a good separation of triphenylphosphine oxide. One tip for its removal is to form its Mg(II) complex, which is poorly soluble in toluene or dichloromethane and can be filtered off. See WO 1998007724.

Coordination chemistry[edit]


Ph3PO is an excellent ligand for "hard" metal centers. A typical complex is the tetrahedral species NiCl2(OPPh3)2.[3]

Ph3PO is a common impurity in PPh3. The oxidation of PPh3 by oxygen, including air, is catalyzed by many metal ions:

2 PPh3 + O2 → 2 Ph3PO


  1. ^ D. E. C. Corbridge "Phosphorus: An Outline of its Chemistry, Biochemistry, and Technology" 5th Edition Elsevier: Amsterdam. ISBN 0-444-89307-5.
  2. ^ M. C. Etter and P. W. Baures (1988). "Triphenylphosphine oxide as a crystallization aid". J. Am. Chem. Soc. 110 (2): 639–640. doi:10.1021/ja00210a076. 
  3. ^ D. M. L. Goodgame and M. Goodgame (1965). "Near-Infrared Spectra of Some Pseudotetrahedral Complexes of Cobalt (II) and Nickel(II)". Inorg. Chem. 4 (2): 139–143. doi:10.1021/ic50024a002. 

Other reading[edit]